This invention relates to die attach adhesives containing resins that contain both vinyl ether and either carbamate, thiocarbamate or urea functionality.
Adhesive compositions, particularly conductive adhesives, are used for a variety of purposes in the fabrication and assembly of semiconductor packages and microelectronic devices. The more prominent uses are the bonding of integrated circuit chips to lead frames or other substrates, and the bonding of circuit packages or assemblies to printed wire boards.
There exist electron acceptor/donor adhesives that contain vinyl ethers as the donor compounds for use in low modulus adhesives, particularly in fast-cure adhesives for die attach applications. However, die attach adhesives containing commercially available vinyl ethers frequently suffer from poor adhesion, resin bleed and voiding due to the volatility and non-polar nature of these commercial vinyl ethers. Thus, there is a need for improved die attach adhesives utilizing vinyl ethers containing polar functionality in order to address these performance issues.
This invention relates to die attach adhesive compositions containing resins that have vinyl ether and polar functionality, such as a carbamate, thiocarbamate or urea functionality, on a molecular (small molecule) or polymeric entity. The die attach adhesive compositions may contain a curing agent and one or more fillers.
The molecular or polymeric group may be a branched, linear, or cyclic alkane, a siloxane, a polysiloxane, a C1 to C4 alkoxy-terminated siloxane or polysiloxane, a polyether, a polyester, a polyurethane, a poly(butadiene), or an aromatic, polyaromatic, or heteroaromatic group.
In another embodiment, this invention is a die attach adhesive composition comprising one or more of the polar vinyl ether compounds and one or more co-polymerizable electron acceptor compounds, and a curing agent and one or more fillers. Suitable electron acceptor compounds for copolymerization are fumarates and maleates, for example, dioctyl maleate, dibutyl maleate, dioctyl fumarate, dibutyl fumarate. Resins or compounds containing acrylate and maleimide functionality are other suitable electron acceptor materials.
The polar vinyl ether compounds used in the die attach adhesive compositions of this invention will be compounds having a structure as depicted here: 
in which
n is 1 to 6, and preferably 1 to 3;
R1, R2, and R3 are hydrogen, methyl or ethyl, preferably two of R1, R2, and R3 are hydrogen and one is methyl, and more preferably all are hydrogen;
Q is a linear or branched chain alkyl or cycloalkyl having 1 to 12 carbon atoms; a linear or branched chain alkylenoxy having 1 to 12 carbon atoms, or an aromatic or heteroaromatic ring or fused ring having 3 to 10 carbon atoms within the ring structure, in which the heteroatoms may be N, O, or S;
X and Y are independently O, NR1, or S, in which R1 is as described above, with the proviso that both X and Y cannot be oxygen or sulfur, and
Z is a branched or linear alkane, which may contain cyclic moieties, a siloxane, a polysiloxane, a C1 to C4 alkoxy-terminated siloxane or polysiloxane, a polyether, a polyester, a polyurethane, a poly(butadiene), or an aromatic, polyaromatic, or heteroaromatic group.
Starting materials for preparation as the Z group are commercially available from a number of sources; for example, aromatic and polyaromatic materials may be obtained from BASF or Bayer; siloxanes and polysiloxanes from Gelest; polyethers from BASF; polyesters from Uniqema or Bayer; poly(butadiene)s from Elf-Atochem; polyurethanes from Bayer or BASF; and the branched or linear alkanes from Uniqema. Some of these sources will have available Z materials already functionalized for reaction with a co-reactive functionality with the starting material containing the vinyl ether group; in other cases, the practitioner will need to functionalize the materials in preparation for reaction with the vinyl ether starting material.
The exact composition or molecular weight of Z is not critical to the invention and can range widely depending on the requirements of the end use for the electron donor compound. The composition of Z can be chosen to give specific material properties in a final formulation, such as, rheological properties, hydrophilic or hydrophobic properties, toughness, strength, or flexibility. For example, a low level of crosslinking and free rotation about polymeric bonds will impart flexibility to a compound, and the presence of siloxane moieties will impart hydrophobicity and flexibility. The molecular weight and chain length will affect viscosity, the higher the molecular weight and the longer the chain length, the higher the viscosity.
These polar vinyl ether compounds can be prepared by various synthetic routes as devised by those skilled in the art. One suitable method is through a condensation or addition reaction between a vinyl ether terminated alcohol, amine or thiol and a co-reactive functionality such as an isocyanate on the molecular or polymeric entity starting material. Synthetic routes for a vinyl ether terminated alcohol, and for a vinyl ether containing urethane oligomers are disclosed in U.S. Pat. Nos. 4,749,807, 4,751,273, and 4,775,732 assigned to Allied Signal, Inc.
These polar vinyl ether compounds can blended with electron acceptor compounds, such as fumarates, maleates, acrylates, and maleimides, for co-polymerization to form cured adhesive compositions for use in a wide variety of applications. Suitable fumarates and maleates are, for example, dioctyl maleate, dibutyl maleate, dioctyl fumarate, dibutyl fumarate. Suitable acrylates are numerous and are commercially available, for example, from Sartomer. Suitable maleimides are easily prepared, for example, according to procedures described in U.S. Pat. Nos. 6,034,194 and 6,034,195 to Dershem.
The inventive polar vinyl ether compounds may be formulated into adhesive, coating, potting or encapsulant compositions, and particularly into compositions for use in electronics applications. The compositions may contain one or more curing agents and conductive or nonconductive fillers, and also stabilizing compounds, adhesion promoters or coupling agents.
In general the adhesive compositions will contain a mixture of the electron donor polar vinyl ether and an electron acceptor. The molar ratio of electron donor to electron acceptor will usually be within the range of 1:2 to 2:1, but other ranges may be suitable for particular end uses. The choice of molar ratio to obtain specific properties in the final cured composition will be within the expertise of one skilled in the art without undue experimentation. The electron donor/acceptor system typically will be present in the adhesive composition at 5 to 30 weight percent for those compositions containing fillers. For compositions that do not contain any fillers, the electron donor/acceptor mixture will be the predominant component.
These compositions may be cured thermally or by radiation. Exemplary curing agents are free-radical initiators and photoinitiators, present in an amount of 0.1% to 10%, preferably 0.1% to 3.0%, by weight of the composition. Preferred free-radical initiators include peroxides, such as butyl peroctoates and dicumyl peroxide, and azo compounds, such as 2,2xe2x80x2-azobis(2-methyl-propanenitrile) and 2,2xe2x80x2-azobis(2-methyl-butanenitrile). A preferred series of photoinitiators is sold under the trademark Irgacure by Ciba Specialty Chemicals. In some formulations, both thermal initiation and photoinitiation may be desirable, for example, the curing process can be started by irradiation, and in a later processing step curing can be completed by the application of heat to accomplish the thermal cure.
In general, these compositions will cure at a temperature within the range of 70xc2x0 C. to 250xc2x0 C., and curing will be effected at a time interval within the range of ten seconds to three hours. The time and temperature curing profile of each formulation will vary with the specific electron donor compound and the other components of the formulation; the parameters of a curing profile can be determined by one skilled in the art without undue experimentation.
Exemplary conductive fillers are carbon black, graphite, gold, silver, copper, platinum, palladium, nickel, aluminum, silicon carbide, boron nitride, diamond, and alumina. Exemplary nonconductive fillers are particles of vermiculite, mica, wollastonite, calcium carbonate, titania, sand, glass, fused silica, fumed silica, barium sulfate, and halogenated ethylene polymers, such as tetrafluoroethylene, trifluoroethylene, vinylidene fluoride, vinyl fluoride, vinylidene chloride, and vinyl chloride. When present, fillers typically will be in amounts of 70% to 95% by weight of the formulation.
Exemplary adhesion promoters or coupling agents are silanes, silicate esters, metal acrylates or methacrylates, titanates, and compounds containing a chelating ligand, such as phosphine, mercaptan, and acetoacetate. When present, coupling agents will be in amounts up to 10% by weight, and preferably in amounts of 0.1% to 3.0% percent by weight of the electron donor compounds.
The formulations may contain compounds that lend additional flexibility and toughness to the resultant cured material. Such compounds may be any thermoset or thermoplastic material having a Tg of 150xc2x0 C. or less, and typically will be a polymeric material, such as, a polyacrylate, poly(butadiene), polyTHF (polymerized tetrahydrofuran), carboxy-terminated butyronitrile rubber and polypropylene glycol. When present, these compounds may be in an amount up to about 15% by weight of the polar vinyl ether compound.
The following examples show representative polar vinyl ether compounds, reactions for their preparation, and adhesive formulations prepared from these compounds. The reaction products were characterized by 1H-NMR and FT-IR spectroscopies. The examples are illustrative of the invention and are not intended as a limitation. by conversion to the diisocyanate derivative. C36 represents the mixture of isomers of linear and branched alkyl chains having 36 carbon atoms (which result from the dimerization of linoleic and oleic acids).